1. Field of the Invention
The present invention relates to a method for manufacturing agglomerates of fired pellets fitted for materials used for a blast furnace or a direct reduction furnace, and more particularly, to conditions on materials used for manufacture of the agglomerates of fired pellets and conditions on pelletization of the materials.
2. Description of the Related Art
As materials used for a blast furnace or a direct reduction furnace, agglomerates of fired pellets, which are made from fine iron ores by pelletization and by sintering are well known. Consumption of these fired pellets are increasing in amount year by year, various research and development on these fired pellets has been performed. For example, a method is disclosed in a Japanese Patent Application Laid Open (KOKAI) No. 106728/86 to which a U.S. patent application Ser. No. 769624 corresponds, wherein:
(a) To fine iron ores mainly composed of those of 5 mm or less in particle size, fluxes are added, and the fine iron ores are pelletized, as the first step pelletization, into green pellets; PA1 (b) the green pellets are coated on their surface, as the second step pelletization, with solid fuels such as powder cokes, powder chars, fine powder coals and powder oil cokes to prepare mini-pellets of 3 to 9 mm in particle size, providing that the addition ratio of the solid fuels is 2.5 to 3.5 wt. % to the fine iron ores; PA1 (c) the mini-pellets are sintered, through a grate type sintering machine equipped with zones for drying, igniting, sintering and cooling, to prepare blocky agglomerates of mini-pellets; PA1 (d) the agglomerates of mini-pellets manufactured by sintering are composed of mini-pellets combined on their surface through work of calcium ferrite. PA1 (1) The yield is low, and, consequently, the productivity is low. PA1 (2) The strength of the agglomerates of mini-pellets is not satisfactory for the operation of a blast furnace and a direct reduction furnace. PA1 the step, as the first pelletization, of adding and mixing fluxes to and with fine iron ores containing 30 to 95 wt. % of 0.125 mm or less fine iron ores in particle size to form a mixture, and to pelletize the mixture into green pellets; PA1 the step, as the second pelletization, of adding powder cokes containing 80 to 100 wt. % of 0.1 mm or less powder cokes in particle size, to the green pellets, in amount of 2.5 to 4.0 wt. % to the powder-iron ores, to prepare, through pelletization, green pellets coated with the powder cokes; and PA1 the step, as sintering, of charging the green pellets coated with the powder cokes into a grate type sintering machine, to sinter the green pellets coated with powder cokes, thereby the agglomerates of fired pellets being produced. PA1 Furthermore, a method is provided for manufacturing agglomerates of fired pellets comprising the steps of: PA1 the step, as the first pelletization, of adding and mixing fluxes to and with fine iron ores containing 10 to 80 wt. % of 0.044 mm or less fine iron ores in particle size, to form a mixture and to pelletize the mixture into green pellets; PA1 the step, as the second pelletization, of adding powder cokes containing 20 to 70 wt. % of 0.1 mm or less in particle size, to the green pellets, in amount of 2.5 to 4.0 wt. % to the fine iron ores, to prepare, through pelletization, green pellets with the powder cokes; and PA1 the step, as sintering, of charging the green pellets coated with the powder cokes into a grate type sintering machine, to sinter the green pellets coated with powder cokes, thereby the agglomerates of fired pellets being produced. PA1 The object and the other objects and advantages of the present invention will become more apparent from the detailed description to follow, taken in conjunction with the appended drawings.
This method, however, allows the following difficulties to remain still unsettled;